1. Field of the Invention
The present invention relates to a semiconductor device and a driving method thereof. Specifically, the present invention relates to a semiconductor device capable of performing power gating and a driving method thereof. Note that a semiconductor device in this specification refers to a device that operates by utilizing semiconductor characteristics.
2. Description of the Related Art
Attention has been paid to power gating as a technique for reducing power consumption of a central processing unit (CPU) or the like. The power gating is a technique for stopping supply of a power source voltage to part or whole of the CPU when part or whole of the CPU does not operate. Accordingly, it is possible to suppress static power consumption (power consumed for maintaining the state of part or whole of the CPU).
For example, Patent Document 1 discloses a semiconductor device in which supply of a power source voltage to a functional circuit (a memory circuit) is controlled by switching a transistor (a power-gating transistor) whose channel is formed in an oxide semiconductor layer. Specifically, in the semiconductor device disclosed in Patent Document 1, power gating is performed as follows: switching or the like of the transistor (power-gating transistor) is controlled on the basis of various signals output from a control circuit (a power-gating control circuit).